The invention pertains to mechanisms for retaining and ejecting standard tool holders in machine tool spindles.
The present invention is especially adapted to operate with conventional tool holders that have been adopted by the American National Standard Institute as the standard tool holder for use in automatic machine tools as specified in ANSI standard B5, TC45. Such tool holders are provided with a tapered shank for reception in a complementary tapered opening in the end of the machine tool spindle. The large end of the taper is adapted to receive a cutting tool for operation on a workpiece while a retention knob extends axially from the small or rear end of the tool holder.
A variety of mechanisms have been designed for cooperating with such retention knob to retain the tool holder in the spindle. For example, the structure shown in U.S. Pat. No. 4,347,753 discloses a collet mounted on the end of a draw bar in position to encompass the knob on the end of the tool. The collet is clamped inwardly to lock the knob to the collet while drawing the tool holder into the spindle. The power for locking the collet and drawing the tool holder tightly into the spindle opening is a stack of Belleville springs disposed within the spindle. The collet is unclamped by hydraulic power which compresses the Belleville springs to release the collet.
However, the prior art retention systems require relatively complex mechanisms mounted within the spindle and necessitate the boring of an axial hole through the spindle as well as other difficult machining operations. The present invention eliminates the requirement for a central bore through the entire spindle and performs the function of locking the tool holder to the spindle without the conventional draw bar that passes through the center of the spindle. Instead, the retention and ejection mechanism of the present invention is disposed about the exterior of the spindle but within the quill of a spindle and quill assembly.
The improved retention and ejection mechanism of the present invention enables the spindle to be of solid construction for more efficient and stable operation. The entire assembly is very compact and occupies the small space between the spindle and the quill when the spindle is journaled in a quill. Accordingly, very little extra room is required in the spindle head which supports the spindle. Moreover, because of its unique arrangement, the mechanism exerts a minimum amount of force on the spindle bearings during its operation to reduce the amount of maintenance required on the entire spindle assembly while increasing its life.
Another advantage of the present invention lies in the fact that since the unit does not extend through a central bore in the spindle there is no operating structure at the rear end of the spindle. This permits the entire spindle head to be of minimum size while enabling it to be of a neat and streamlined design for enhancing the appearance of the machine.
Moreover, the arrangement is such, that the force repeated on the retention knob for drawing the tool holder into the spindle and retaining it in the spindle is always concentric with the retention knob even when the latter may be out of concentricity with the tool holder and therefore with the spindle.